Column switching technique

Figure 5.4 Schematic diagrams of a heait-cut valve configuration system. Reprinted from Journal of Chromatography, 602, S. R. Villasenor, Matrix elimination in ion cliromatography by heart-cut column switching techniques , pp. 155-161, copyright 1992, with permission from Elsevier Science.

K. Yamashita, M. Motohashi and T. Yashiki, Column-switching techniques for high-performance liquid cliromatography of ibuprofen and mefenamic acid in human serum with shoit-wavelength ultraviolet detection , J. Chromatogr. 570 329-338 (1991). 

Hutta, M., Rybar, I., Chalanyova, M. (2002). Liquid chromatographic method development for determination of fungicide enantiomers by achiral and chiral column switching technique in water and soil. J. Chromatogr. A 959, 143-152. 

In some cases, so called direct plasma injection techniques may be used23 83 104 108 instead of protein precipitation for loading plasma samples onto an HPLC/MS/MS system. Some direct plasma injection systems use a column switching technique in which the plasma is loaded onto an extraction column that retains the small molecules. The other plasma components are sent to waste and the flow is switched so that the small molecules are eluted onto an analytical column that connects to the MS/MS.23 83 108 One variation of the column switching method is turbulent flow chromatography commercialized by Cohesive Technologies (now part of Thermo, San Jose, CA).23... 

Egle, H. et al. 2005. Fast, fully automated analysis of voriconazole from serum by LC-LC-ESI-MS-MS with parallel column switching technique. J Chromatogr B. 814 361. 

Increasing the concentration of the counter-ion further increased the retention, but the retention reached a plateau, as seen in Figure 4.14. A total separation of the amino acids by reversed-phase ion-pair liquid chromatography could be performed.11 A column switching technique reduced the total analysis time (Figure 4.15). 

Some applications also involved direct injection techniques in which BZDs are preferentially absorbed onto a precolumn and are back-flushed onto the analytical column using column switching techniques (Lauber et al., 1994 Iwase et al., 1994). 

Ary K, Rona K, Ondi S, Gachalyi B. 1998. High-performance liquid chromatographic method with coulometric detection for the determination of buspirone in human plasma by means of a column-switching technique. J Chromatogr A 797(1-2) 221-226. 

MDGC is useful for separating compounds of an essential oil using two columns in line with different polarities. Through column-switching techniques, selected impure compounds in the first column can be diverted to the second column to ensure their complete separation. If the second column is chiral, then enantiomers potentially can be separated. The selected chiral stationary phase affects the resolution and separation drastically [73]. 

Using immobilized -glucuronidase reactors, estriol and estradiol glucuronides have been determined in urine by a column-switching technique (270, 271). Both glucuronides were hydrolyzed by the immobilized enzyme at pH 7. The steroid mixture was subsequently separated by gradient elution on a reversed-phase column, to be finally detected by UV absorbance at 280 nm. In this procedure, the activity of enzyme did not alter even after 150 h continuous run and exposure to a mobile phase containing 10% methanol. When a separate reversed-phase precolumn was inserted in the LC system, additional sample purification and shorter analysis time could be attained (272). 

To eliminate or reduce interference and concentrate the analyte(s), the primary sample extract can further be subjected to various types of cleanup procedures including liquid-liquid partitioning, solid-phase extraction, immunoaffmity chromatography, and column-switching techniques (Table 29.17). In some instances, more than one of these procedures may be used in combination to enhance the cleanup efficiency. 

JJ Bekhof, JW van den Bedem. Study on the determination of vitamin D in fortified milk, milk powder and infant formula by HPLC using a column switching technique. Neth Milk Dairy J 42 423-435, 1988. 

A schematic diagram of a heart-cut LC-LC system is depicted in Figure 5.4. The column switching technique was developed by employing two high-pressure four-way pneumatic valves inserted before and after the precolumn (39). The front-cut and the end-cut of the sample eluted from the first column were vented to waste. The valves were manipulated to transfer only the heart-cut of the analyte of interest to the analytical column. The detailed operational conditions for the four-step sequence of this system can be described as follows ... 

S. R. Villasenor, Heart-cut column switching techniques for the determination of an aliphatic amine in an organic matrix and for low levels of sulfate in an anion matrix , J. Chromatogr. 671 11-14(1994). 

Y. Odd, H. Ohe, S. Tanaka, N. Asakawa, Direct determination of E2020 enantiomers in plasma by liquid chromatography-mass spectrometry and column-switching techniques, J. Chromatogr. A. 694 (1995) 209-218. 

D. Dadgar and A. Power, Applications of column-switching technique in biopharmaceutical analysis. I. High-performance liquid chromatographic determination of amitriptyline and its metabolites in human plasma, J. Chromatogr., 416 99 (1987). 

The other form of on-line solid-phase extraction procedures involves column-switching techniques. Column switching employs valves that can be switched manually or automatically between a number of columns at predetermined times.67-69 For sample cleanup the analyte of interest is retained on the primary or precolumn while the interfering matrix components are eluted to waste. The analytes are then diverted to a second or analytical column where they are separated for identification and quantification. 

Table 3.11 Advantages and Disadvantages of Column-Switching Techniques for Sample Cleanup3...

---